Refining and purifying method of high-purity 3, 5-dichlorobenzonitrile

Abstract

The invention relates to the technical field of compound purification, and particularly discloses a refining and purifying method of high-purity 3, 5-dichlorobenzonitrile, which comprises the following specific steps: (1) adding a 3, 5-dichlorobenzonitrile crude product and a depolymerizing agent into a mixed solvent consisting of an organic solvent and water, heating, stirring and dissolving for a period of time, so that a dimer is converted into 3, 5-dichlorobenzamide; (2) cooling and crystallizing, dissolving 3, 5-dichlorobenzamide in the solvent, and separating out 3, 5-dichlorobenzonitrile; and (3) carrying out solid-liquid separation to obtain purified 3, 5-dichlorobenzonitrile. Wherein the dimer is a dimer of 3, 5-dichlorobenzamide, and the depolymerizing agent is a water-soluble weakly alkaline inorganic salt. According to the purification method provided by the invention, dimer impurities in the 3, 5-dichlorobenzonitrile can be effectively removed, and the purity of the 3, 5-dichlorobenzonitrile is improved to 99.9% or above.

Description

Technical Field

[0001] This application relates to the field of compound purification technology, and more specifically, it relates to a method for purifying high-purity 3,5-dichlorobenzonitrile. Background Technology

[0002] 3,5-Dichlorobenzonitrile is an important intermediate in pesticides, pharmaceuticals, and polymer materials, and its purity directly affects the performance and quality of downstream products. Especially in high-end applications, the purity requirements for 3,5-dichlorobenzonitrile are extremely high.

[0003] The main synthetic routes for 3,5-dichlorobenzonitrile are direct chlorination and amide dehydration, especially the amide dehydration method. Specifically, 3,5-dichlorobenzoamide is dehydrated in the presence of dehydrating agents such as phosphorus oxychloride or trifluoromethanesulfonic acid to produce 3,5-dichlorobenzonitrile. The process route is as follows: .

[0004] This process route is low-cost, high-capacity, and has broad market prospects. However, the purity of the product obtained by this process is consistently around 98-99%, which is insufficient to meet high-purity requirements. The inventors conducted in-depth research on the above process route and performed qualitative analysis of impurities. They discovered that a dimer impurity with a molecular structure similar to the target product is readily generated in the acidic dehydration reaction pathway of formamide. The structural formula of this dimer impurity is as follows: It is a symmetrical molecule composed of two 3,5-dichlorobenzoyl groups linked by a central amide bond (-CO-NH-CO-). Because this dimer impurity has extremely similar physicochemical properties to the target product 3,5-dichlorobenzonitrile, such as molecular weight, boiling point, polarity, and solubility in common organic solvents, traditional purification methods face significant challenges.

[0005] In existing technologies, the purification of 3,5-dichlorobenzonitrile typically employs methods such as recrystallization, vacuum distillation, or column chromatography. However,

[0006] Recrystallization method: The separation efficiency is low, the removal effect of the above-mentioned dimer impurities is very poor, and multiple repeated operations are required to slightly improve the purity. The yield loss is serious and cannot meet the needs of industrial-scale high-purity product production.

[0007] Vacuum distillation: Since the boiling points of the two are similar, azeotropes are easily formed during the separation process, resulting in limited improvement in product purity. Furthermore, high-temperature environments may cause product decomposition or further condensation of dimer impurities, posing safety risks.

[0008] Column chromatography: Although it can achieve high purity, this method is expensive and cumbersome to operate, and is only suitable for small-scale preparation in the laboratory. It is not feasible for industrial scale-up at all.

[0009] Therefore, there is an urgent need in this field to develop a purification method for high-purity 3,5-dichlorobenzonitrile that is highly specific, easy to operate, low in cost, and suitable for large-scale industrial production. This method should be able to efficiently and selectively remove dimer impurities with properties highly similar to the product, thereby consistently obtaining a product with a purity higher than 99.9%. Summary of the Invention

[0010] To address the aforementioned technical problems, this application provides a purification method for high-purity 3,5-dichlorobenzonitrile. This purification method can effectively remove dimer impurities from 3,5-dichlorobenzonitrile and improve the purity of 3,5-dichlorobenzonitrile to over 99.9%.

[0011] The purification method for high-purity 3,5-dichlorobenzonitrile provided in this application adopts the following technical solution:

[0012] A method for refining and purifying high-purity 3,5-dichlorobenzonitrile includes the following steps:

[0013] (1) Add crude 3,5-dichlorobenzonitrile and depolymerizing agent to a mixed solvent of organic solvent and water, heat and stir to dissolve for a period of time, so that the dimer is converted into 3,5-dichlorobenzoamide;

[0014] (2) Cooling and crystallization to dissolve 3,5-dichlorobenzamide in the solvent and precipitate 3,5-dichlorobenzonitrile;

[0015] (3) Solid-liquid separation was performed to obtain purified 3,5-dichlorobenzonitrile.

[0016] The dimer is a dimer of 3,5-dichlorobenzamide, with the following structural formula: The depolymerizing agent is a water-soluble, weakly basic inorganic salt.

[0017] The term "water-soluble" as used in this application refers to a substance whose solubility in water at room temperature (25°C) is sufficient to allow it to be effectively removed from the organic phase by a water washing step after the reaction.

[0018] This application introduces a water-soluble, weakly basic inorganic salt as a depolymerizing agent to selectively catalyze the hydrolysis of dimer impurities to 3,5-dichlorobenzamide in a suitable solvent system. This product, due to its significantly increased polarity, is stably soluble in the solvent phase, while the target product, 3,5-dichlorobenzonitrile, precipitates efficiently during cooling due to its decreased solubility. After solid-liquid separation, the target product with a purity exceeding 99.9% can be directly obtained without multiple repeated processing steps. This process avoids the decomposition risks associated with high-temperature distillation and circumvents the high cost and low throughput issues of column chromatography. It offers advantages such as mild reaction conditions, simple operation, high yield, and environmental friendliness, making it particularly suitable for continuous industrial production. The above impurity removal mechanism is as follows: .

[0019] More preferably, in the crude 3,5-dichlorobenzonitrile, the molar ratio of 3,5-dichlorobenzonitrile to the depolymerizing agent is 1:0.008 to 1:0.021.

[0020] HPLC analysis can be used to quantify the dimer in crude 3,5-dichlorobenzonitrile. Combined with process parameter optimization, the optimal molar ratio for the depolymerization reaction is determined to be 1:0.008 to 1:0.021. This molar ratio range can ensure that the depolymerization reaction proceeds fully, while avoiding the introduction of additional impurities or increased burden on subsequent separation due to excessive depolymerizing agent.

[0021] More preferably, the depolymerizing agent is a water-soluble bicarbonate or carbonate, including but not limited to: sodium carbonate, sodium bicarbonate, potassium carbonate, etc.

[0022] Bicarbonates and carbonates are weakly alkaline, which can effectively control the product from undergoing secondary hydrolysis when reacting with dimer impurities. This avoids the strong alkalinity that causes 3,5-dichlorobenzonitrile to hydrolyze into the corresponding amide, or even to continue hydrolyzing and generating new impurities.

[0023] More preferably, the organic solvent is one of acetonitrile, dioxane, and tetrahydrofuran.

[0024] This mixed solvent effectively dissolves crude 3,5-dichlorobenzonitrile while providing a suitable polar environment for the depolymerization reaction, promoting the hydrolysis and transformation of dimer impurities, and dissolving the 3,5-dichlorobenzoamide product after hydrolysis of the dimer impurities, thus improving the purity of the target product. Furthermore, the presence of water in the mixed solvent can reduce the solubility of the target product to some extent, further increasing its yield. The aforementioned preferred organic solvent exhibits good miscibility with water and moderate polarity, effectively dissolving dimer impurities and stabilizing the 3,5-dichlorobenzoamide product from the hydrolysis of the dimer impurities. Simultaneously, it significantly reduces the solubility of 3,5-dichlorobenzonitrile during the cooling stage, promoting its selective precipitation.

[0025] More preferably, the mass ratio of the organic solvent to water is 1:3 to 1:5.

[0026] The ratio of organic solvent to water significantly affects the impurity removal efficiency and the yield of the target product. Excessive solvent affects the solubility of the depolymerizing agent in the mixed solvent, leading to incomplete impurity removal or prolonged removal time; excessive water causes 3,5-dichlorobenzonitrile to encapsulate impurities during precipitation, affecting purity. Therefore, controlling the mass ratio of organic solvent to water within the range of 1:3 to 1:5 can balance depolymerization efficiency and product precipitation selectivity, achieving synergistic optimization of high purity and high yield.

[0027] In summary, this application has the following beneficial effects:

[0028] This application utilizes a depolymerizing agent to convert impurity dimers in 3,5-dichlorobenzonitrile into 3,5-dichlorobenzamide, followed by separation of the two by cooling crystallization and filtration. This achieves the purification of 3,5-dichlorobenzonitrile, yielding a product with a purity of up to 99.9% and a stable yield exceeding 90%. The process is mild, simple to operate, and suitable for industrial-scale production. The depolymerizing agent used is a water-soluble bicarbonate or carbonate, and the solvents used are all conventional chemicals, resulting in low cost and environmental friendliness. Attached Figure Description

[0029] Figure 1 The high-performance liquid chromatogram of 3,5-dichlorobenzonitrile purified using the process steps in Example 1 of this application is shown.

[0030] Figure 2 The high-performance liquid chromatogram of 3,5-dichlorobenzonitrile purified using the process steps of Example 2 of this application is shown.

[0031] Figure 3 The high-performance liquid chromatogram of 3,5-dichlorobenzonitrile purified using the process steps in Example 3 of this application is shown.

[0032] Figure 4 The high-performance liquid chromatogram of 3,5-dichlorobenzonitrile purified using the process steps in Example 4 of this application is shown.

[0033] Figure 5 The high-performance liquid chromatogram of 3,5-dichlorobenzonitrile purified using the process steps in Example 5 of this application is shown.

[0034] Figure 6 The high-performance liquid chromatogram of 3,5-dichlorobenzonitrile purified using the process steps in Example 6 of this application is shown.

[0035] Figure 7 The high-performance liquid chromatogram of 3,5-dichlorobenzonitrile purified using the process steps in Example 7 of this application is shown.

[0036] Figure 8 The high-performance liquid chromatogram of 3,5-dichlorobenzonitrile purified using the process steps of Comparative Example 1 of this application is shown.

[0037] Figure 9 The high-performance liquid chromatogram of 3,5-dichlorobenzonitrile purified using the process steps of Comparative Example 2 of this application is shown.

[0038] Figure 10 The high-performance liquid chromatogram of 3,5-dichlorobenzonitrile purified using the process steps of Comparative Example 3 of this application is shown. Detailed Implementation

[0039] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application.

[0040] Furthermore, it should be understood that the one or more method steps mentioned in this application do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of the method steps or limit the scope of implementation of this application. Changes or adjustments to their relative relationships, without substantially altering the technical content, shall also be considered as within the scope of implementation of this application.

[0041] Unless otherwise specified, the experimental conditions used in the examples are generally in accordance with conventional conditions in the art or the conditions recommended by the reagent company. Unless otherwise specified, the materials and reagents used in the examples can be purchased commercially.

[0042] Preparation Example

[0043] Preparation Example 1: Preparation of crude 3,5-dichlorobenzonitrile

[0044] 100g of 3,5-dichlorobenzamide, 300g of acetonitrile, and 80g of phosphorus oxychloride were added to a 500ml four-necked flask. The mixture was then heated to reflux and reacted for 3 hours. The temperature was then lowered to 20–30°C, and 1550g of water was added dropwise to quench the reaction. The mixture was filtered and dried under vacuum to obtain 81g of 3,5-dichlorobenzamide. HPLC analysis showed a purity of 98.44%, with a dimer content of 1.3%.

[0045] Preparation Example 2: Preparation of crude 3,5-dichlorobenzonitrile

[0046] 200 kg of 3,5-dichlorobenzamide, 600 kg of acetonitrile, and 160 kg of phosphorus oxychloride were added to a 2000 L glass-lined reactor. The mixture was then heated to reflux and reacted for 3 hours. The temperature was then lowered to 20–30 °C, and the reaction was quenched by adding 3100 kg of water dropwise. After filtration and vacuum drying, 166 kg of 3,5-dichlorobenzonitrile was obtained. HPLC analysis showed a purity of 98.44%, with a dimer content of 1.3%.

[0047] Example

[0048] Example 1 Purification of 3,5-dichlorobenzonitrile

[0049] 81 g of crude 3,5-dichlorobenzonitrile prepared according to the process in Preparation Example 1 was added to a 500 ml reaction flask, along with 243 g of acetonitrile and 729 g of water (acetonitrile:water mass ratio = 1:3), and then 0.8 g of sodium bicarbonate. The mixture was heated to reflux and stirred for 3 h. Then, the temperature was lowered to 10–20 °C, stirred for 30 min, filtered, and dried to obtain 73 g of high-purity 3,5-dichlorobenzonitrile, with a yield of 90.12%. HPLC analysis showed the following results. Figure 1 As shown, the retention time of the main peak was 7.905 min, accounting for 99.935%. There were no obvious impurity peaks near the main peak, except for a very small impurity peak at 3.868 min, accounting for 0.065%. This indicates that the above purification process can effectively remove dimers and other trace impurities from 3,5-dichlorobenzonitrile, significantly improving the purity of the product.

[0050] Example 2 Purification of 3,5-dichlorobenzonitrile

[0051] The difference from Example 1 is that the process was scaled up for production verification. The specific process steps are as follows:

[0052] 100 kg of crude 3,5-dichlorobenzonitrile prepared according to the process in Preparation Example 2 was added to a 1500 L glass-lined reactor, along with 300 kg of acetonitrile and 900 kg of water (acetonitrile:water mass ratio = 1:3), and then 0.99 kg of sodium bicarbonate. The mixture was heated to reflux and stirred for 3 h. Then, the temperature was lowered to 10–20 °C, stirred for 30 min, filtered, and dried to obtain 92 kg of high-purity 3,5-dichlorobenzonitrile, with a yield of 92%. HPLC analysis showed the following results. Figure 2 As shown, the retention time of the main peak was 7.940 min, accounting for 99.9372%. There were no obvious impurity peaks near the main peak, with only very small impurity peaks at 3.919 min and 103.68 min, accounting for 0.0319% and 0.0309% respectively. This indicates that even in a 100 kg scale-up process, the dimer and other impurities in 3,5-dichlorobenzonitrile can still be effectively removed. The product purity is stable and the yield is excellent, proving that the process has good scalability and stability for industrial production, and has good prospects for industrial application.

[0053] Example 3 Purification of 3,5-dichlorobenzonitrile

[0054] The difference from Example 1 is that sodium carbonate is used instead of sodium bicarbonate as the depolymerizing agent, and its molar ratio with 3,5-dichlorobenzonitrile is reduced. The specific process steps are as follows:

[0055] 81 g of crude 3,5-dichlorobenzonitrile prepared according to the process in Preparation Example 1 was added to a 500 ml reaction flask, along with 243 g of acetonitrile and 729 g of water (mass ratio of acetonitrile:water = 1:3), and then 0.4 g of sodium carbonate. The mixture was heated to reflux and stirred for 3 h. Then, the temperature was lowered to 10–20 °C, stirred for 30 min, filtered, and dried to obtain 73 g of high-purity 3,5-dichlorobenzonitrile, with a yield of 90.12%. HPLC analysis showed the following results. Figure 3 As shown, the retention time of the main peak was 7.894 min, accounting for 99.95%. There were no obvious impurity peaks near the main peak, with only very small impurity peaks at 3.862 min and 10.345 min, accounting for 0.017% and 0.033% respectively. This indicates that using sodium carbonate as a depolymerizing agent, the purification process can still effectively remove dimers and other trace impurities from 3,5-dichlorobenzonitrile, significantly improving product purity.

[0056] Example 4 Purification of 3,5-dichlorobenzonitrile

[0057] The difference from Example 1 is that the mixed solvent is composed of dioxane and water, and the mass ratio of the mixed solvent to the crude product is the same. The specific process steps are as follows:

[0058] 81 g of crude 3,5-dichlorobenzonitrile prepared according to the process in Preparation Example 1 was added to a 500 ml reaction flask, along with 243 g of dioxane and 729 g of water (dioxane:water mass ratio = 1:3), and then 0.8 g of sodium bicarbonate. The mixture was heated to reflux and stirred for 3 h. Then, the temperature was lowered to 10–20 °C, stirred for 30 min, filtered, and dried to obtain 72.9 g of high-purity 3,5-dichlorobenzonitrile, with a yield of 90%. HPLC analysis showed the following results. Figure 4 As shown, the retention time of the main peak was 7.880 min, accounting for 99.9055%. There were no obvious impurity peaks near the main peak, with only very small impurity peaks at 3.844 min and 10.330 min, accounting for 0.005781% and 0.0887% respectively. This indicates that using a mixed solution of dioxane and water as the reaction solvent, the purification process can still effectively remove dimers and other trace impurities from 3,5-dichlorobenzonitrile, significantly improving the purity of the product.

[0059] Example 5 Purification of 3,5-dichlorobenzonitrile

[0060] The difference from Example 1 is that the mixed solvent consists of tetrahydrofuran and water, potassium carbonate is used instead of sodium bicarbonate as the depolymerizing agent, and the molar ratio of the depolymerizing agent to 3,5-dichlorobenzonitrile in the crude product is the same. The specific process steps are as follows:

[0061] 81 g of crude 3,5-dichlorobenzonitrile prepared according to the process in Preparation Example 1 was added to a 500 ml reaction flask, along with 243 g of tetrahydrofuran and 729 g of water (tetrahydrofuran:water = 1:3 by mass), and then 0.97 g of potassium carbonate. The mixture was heated to reflux and stirred for 3 h. Then, the temperature was lowered to 10–20 °C, stirred for 30 min, filtered, and dried to obtain 75.6 g of high-purity 3,5-dichlorobenzonitrile, with a yield of 93.33%. HPLC analysis showed... Figure 5 As shown, the retention time of the main peak was 7.793 min, accounting for 99.9104%. There were no obvious impurity peaks near the main peak, with only a very small impurity peak at 3.75 min, accounting for 0.0896%. This indicates that using tetrahydrofuran and water as a mixed solvent and potassium carbonate as a depolymerizing agent, the purification process can still effectively remove dimers and other trace impurities from 3,5-dichlorobenzonitrile, significantly improving the purity of the product.

[0062] Example 6 Purification of 3,5-dichlorobenzonitrile

[0063] The difference from Example 1 is that in the mixed solvent, the mass ratio of acetonitrile to water is 1:5, and the mass ratio of the mixed solvent to the crude product is the same. The specific process steps are as follows:

[0064] 81 g of crude 3,5-dichlorobenzonitrile prepared according to the process in Preparation Example 1 was added to a 500 ml reaction flask, along with 162 g of acetonitrile and 810 g of water (acetonitrile:water mass ratio = 1:5), and then 0.8 g of sodium bicarbonate. The mixture was heated to reflux and stirred for 3 h. Then, the temperature was lowered to 10–20 °C, stirred for 30 min, filtered, and dried to obtain 56.7 g of high-purity 3,5-dichlorobenzonitrile, with a yield of 70%. HPLC analysis showed the following results. Figure 6 As shown, the retention time of the main peak was 7.812 min, accounting for 99.929%. There were no obvious impurity peaks near the main peak, except for a very small impurity peak at 3.759 min, accounting for 0.071%. This indicates that when the proportion of water in the mixed solvent is increased, the yield of 3,5-dichlorobenzonitrile obtained by this purification process decreases, but it can still effectively remove dimers and other trace impurities, significantly improving the purity of the product.

[0065] Example 7 Purification of 3,5-dichlorobenzonitrile

[0066] The difference from Example 1 is that potassium bicarbonate is used instead of sodium bicarbonate as the depolymerizing agent, and the molar ratio of the depolymerizing agent to 3,5-dichlorobenzonitrile is the same. The specific process steps are as follows:

[0067] 81 g of crude 3,5-dichlorobenzonitrile prepared according to the process in Preparation Example 1 was added to a 500 ml reaction flask, along with 243 g of acetonitrile and 729 g of water (acetonitrile:water mass ratio = 1:3), and then 0.71 g of potassium bicarbonate. The mixture was heated to reflux and stirred for 3 h. Then, the temperature was lowered to 10–20 °C, stirred for 30 min, filtered, and dried to obtain 57 g of high-purity 3,5-dichlorobenzonitrile, with a yield of 70.37%. HPLC analysis showed the following results. Figure 7 As shown, the retention time of the main peak was 7.789 min, accounting for 99.9119%. There were no obvious impurity peaks near the main peak, except for a very small impurity peak at 3.743 min, accounting for 0.0881%. This indicates that when potassium bicarbonate is used as a depolymerizing agent, the purification process can still effectively remove dimers and other trace impurities from 3,5-dichlorobenzonitrile, significantly improving the purity of the product.

[0068] Comparative Example

[0069] Comparative Example 1: Purification of 3,5-dichlorobenzonitrile

[0070] The difference from Example 1 is that sodium hydroxide is used instead of sodium bicarbonate as the depolymerizing agent, while the molar ratio is the same as in Example 1. The specific process steps are as follows:

[0071] 81 g of crude 3,5-dichlorobenzonitrile prepared according to the process in Preparation Example 1 was added to a 500 ml reaction flask, along with 243 g of acetonitrile and 729 g of water (acetonitrile:water mass ratio = 1:3), and then 0.38 g of sodium hydroxide. The mixture was heated to reflux and stirred for 3 h. Then, the temperature was lowered to 10–20 °C and stirred for 30 min. The mixture was filtered and dried to obtain 75 g of 3,5-dichlorobenzonitrile, with a yield of 92.6%. HPLC analysis showed the following results. Figure 8 As shown, no dimer was detected, but the crude 3,5-dichlorobenzonitrile was not only not purified, but also underwent a severe decomposition reaction, resulting in a sharp drop in the content of the main product to 27.36%, and the generation of a large number of new impurities.

[0072] Comparative Example 2: Purification of 3,5-dichlorobenzonitrile

[0073] The difference from Example 1 is that no depolymerizing agent was added; recrystallization was carried out using only an acetonitrile-water mixed solvent. The specific process steps are as follows:

[0074] 81 g of crude 3,5-dichlorobenzonitrile prepared according to the process in Preparation Example 1 was added to a 500 ml reaction flask, along with 243 g of acetonitrile and 729 g of water (acetonitrile:water = 1:3 by mass). The mixture was heated to reflux and stirred for 3 h. Then, the temperature was lowered to 10–20 °C, stirred for 30 min, filtered, and dried to obtain 71 g of 3,5-dichlorobenzonitrile, with a yield of 87.65%. HPLC analysis showed the following results. Figure 9 As shown, the content of 3,5-dichlorobenzonitrile was 98.44%, and the content of dimer was 1.3%, which was consistent with the purity of the crude product before purification. This indicates that without the addition of a depolymerizing agent, recrystallization by acetonitrile-water mixed solvent alone cannot effectively remove dimers and other impurities from the crude product.

[0075] Comparative Example 3: Purification of 3,5-dichlorobenzonitrile

[0076] The difference from Example 1 is that an equal mass of acetonitrile is used instead of the acetonitrile-water mixed solvent as the recrystallization solvent. The specific process steps are as follows:

[0077] 81 g of crude 3,5-dichlorobenzonitrile prepared according to the process in Example 1 was added to a 500 ml reaction flask, followed by 972 g of acetonitrile and 0.8 g of sodium bicarbonate. The mixture was heated to reflux and stirred for 3 h. Then, the temperature was lowered to 10–20 °C, stirred for 30 min, filtered, and dried to obtain 40 g of 3,5-dichlorobenzonitrile, with a yield of 49.4%. HPLC analysis showed the following results. Figure 9 As shown, the content of 3,5-dichlorobenzonitrile was 98.24%, and the content of dimer was 0%. Compared with before purification, the content of dimer was not detected, but the purity of 3,5-dichlorobenzonitrile did not change, and the yield decreased significantly.

[0078] Results analysis:

[0079] 1) Combining the purification processes and results of Examples 1-7 and Comparative Examples 1-3, it can be seen that the use of a depolymerizing agent, carbonate / bicarbonate, and a water-containing mixed solvent can effectively remove the dimer, so that the purity of 3,5-dichlorobenzonitrile can reach more than 99.9%.

[0080] 2) Combining the purification process and purification results of Example 1 and Comparative Example 1, it can be seen that if a strong base is used instead of bicarbonate or carbonate, although the dimer impurities can be eliminated, the product 3,5-dichlorobenzonitrile will also be decomposed into the raw material 3,5-dichlorobenzoamide, resulting in a significant reduction in product and purity.

[0081] 3) Combining the purification process and purification results of Example 1 and Comparative Example 2, it can be seen that when no depolymerizing agent is added, recrystallization using only acetonitrile-water mixed solvent can precipitate crystals, but it cannot effectively break the dimer structure, resulting in impurity residues. The purity of 3,5-dichlorobenzonitrile did not change significantly before and after purification, and the purification effect was limited.

[0082] 4) Combining the purification process and purification results of Example 1 and Comparative Example 3, it can be seen that if a pure organic solvent is used instead of a mixed solvent containing water, the purity of the obtained product is not improved. Although the dimer is removed, the yield is only 49.4%.

[0083] 5) Combining the purification process and purification results of Examples 1 to 3, it can be seen that when the molar amount of depolymerizing agent bicarbonate or carbonate is 0.008 to 0.021 times that of 3,5-dichlorobenzonitrile in crude product, 3,5-dichlorobenzonitrile with a purity of over 99.9% can be obtained. Furthermore, when the feed amount is scaled up to over 100 kg, 3,5-dichlorobenzonitrile products with the same purity and yield as those in the small-scale test can still be obtained, indicating that the process can be industrialized.

[0084] 6) Combining the purification processes and results of Examples 1, 3, 5 and 7, it can be seen that when the depolymerizing agent is changed from sodium bicarbonate to sodium carbonate, potassium bicarbonate or potassium carbonate, a 3,5-dichlorobenzonitrile product with a purity of over 99.9% can still be obtained.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for refining and purifying high-purity 3,5-dichlorobenzonitrile, characterized in that, Includes the following steps: (1) Add crude 3,5-dichlorobenzonitrile and depolymerizing agent to a mixed solvent of organic solvent and water, heat and stir to dissolve for a period of time, so that the dimer is converted into 3,5-dichlorobenzoamide; (2) Cooling and crystallization to dissolve 3,5-dichlorobenzamide in the solvent and precipitate 3,5-dichlorobenzonitrile; (3) Solid-liquid separation was performed to obtain purified 3,5-dichlorobenzonitrile; The dimer is a dimer of 3,5-dichlorobenzamide, with the following structural formula: The depolymerizing agent is a water-soluble, weakly basic inorganic salt.

2. The refining and purification method according to claim 1, characterized in that, In the crude 3,5-dichlorobenzonitrile, the molar ratio of 3,5-dichlorobenzonitrile to the depolymerizing agent is 1:0.008 to 1:0.

021.

3. The refining and purification method according to claim 1, characterized in that, The depolymerizing agent is a water-soluble bicarbonate or carbonate.

4. The refining and purification method according to claim 3, characterized in that, The depolymerizing agent is one of sodium bicarbonate, potassium bicarbonate, sodium carbonate, and potassium carbonate.

5. The refining and purification method according to claim 1, characterized in that, The organic solvent is one of acetonitrile, dioxane, and tetrahydrofuran.

6. The refining and purification method according to claim 1, characterized in that, The mass ratio of the organic solvent to water is 1:3 to 1:

5.

7. The refining and purification method according to claim 1, characterized in that, In step (1), the temperature is raised to the reflux temperature of the mixed solution.

8. The refining and purification method according to claim 7, characterized in that, The reflux reaction time is 1 to 3 hours.

9. The refining and purification method according to claim 1, characterized in that, In step (2), the temperature for cooling crystallization is 10-20°C.

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